As a method for detecting an end point of etching in plasma etching, conventionally, it is known that which is disclosed in Patent Document 1.
In this end-point detection method, a silicon substrate is formed thereon with a mask in which a plurality of etching end-point detection patterns formed of an aperture area and a mask area are drawn, the plurality of etching end-point detection patterns are irradiated with a laser beam, an interference intensity which is generated from an optical path difference of two optical paths in the aperture area and the mask area in each detection pattern and which corresponds to an etching depth is monitored, a change amount of the etching depth, i.e., an etching rate, is calculated based on the monitored interference intensity, and from the calculated etching rate and a lapsed time, an etching end point is detected.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2005-38896